(1) Field of the Invention
This invention relates to a novel infrared absorbent for absorbing near infrared rays having a wavelength of 700-1500 nm or far infrared rays and also relates to an infrared absorbing material using the infrared absorbent such as an optical filter and an optical information recording medium.
(2) Description of the Prior Art
Examples of applications of metal complexes to the infrared absorbent can be found in U.S. Pat. Nos. 3,588,216; 3,663,089; 3,850,502; 3,875,199; 3,979,583; 4,062,867; 4,152,332; and 4,335,952; Japanese Patent Publication Nos. 3452/71 and 7454/77; and Japanese Patent Application (OPI) Nos. 31748/74, 135886/76, 25060/79 and 21458/82.
However, the infrared absorbent of metal complexes as disclosed in the above references mostly has an absorption maximum at a long wavelength of 850 nm or more. Further, to prepare the metal complexes having an absorption maximum at 800 nm or less, it was required to employ an expensive metal such as platinum, and it was difficult to produce the metal complex industrially.
Further, conventional infrared absorbents of organic dyestuffs were not sufficient in light and heat fastness in general, and thus most of them were not satisfactory in practical use.
Heretofore, various applications of an infrared absorbing material capable of selectively absorbing rays of a far infrared light or a near infrared light having a wavelength of 700-1500 nm has been proposed. The following is five examples of conventional primary applications of the infrared absorbing material.
(1) Safelight filter for infrared-sensitive materials:
Recently, there have been developed many silver halide light sensitive materials (which will be hereinafter referring to as "light sensitive materials") which are sensitive to rays of a far infrared light or a near infrared light having a wavelength of 700 nm or more. That is, light sensitive materials are made to have an infrared sensitivity irrespective of distinction of black and white photographs or color photographs including a normal-type, instant-type and thermal developed-type photographs, so as to be useful for an artificial color photograph for resource search or to be exposable with a light emission diode capable of emitting a light in an infrared area.
Conventionally, a safelight filter for a panchromatic photosensitive material has been used as such infrared-sensitive materials.
(2) Control of growth of plants:
It has been long known that a so-called morphogenesis with regard to growth and differentiation of plants such as germination of seed, extension of stem, development of leaf, budding of flower and formation of tuber is influenced by a light, and it has been studied as a photomorphogenesis. It is also known that a red light having a wavelength of about 660 nm and a red light having a wavelength of about 720-730 nm antagonistically function to each other, and therefore time of flowering or earing, extent of growth or yield of fruits can be varied by changing a proportion of both the lights. Such a study has been made by controlling a spectral energy distribution of a light with use of a light source lamp and a filter in combination. Therefore, it was difficult to carry out a test in a large-scale green house or farm.
If a plastic film capable of selectively absorbing rays having a wavelength of 700 nm or more is obtainable, it will be possible to control a spectral energy distribution of a light to adapt the above-mentioned principle to an actual product cite, thereby providing a great progress and profit to an equipped agriculture. For example, it is expected that earing time may be delayed or growth may be controlled by covering plants with a near-infrared absorbing film at a specific time to cut-off light having a wavelength of 700 nm or more. (See "Chemical Control of Plants", Katsumi Ineda, Vol. 6, No. 1 (1971))
(3) Cut-off of heat radiation:
Among solar radient energy rays of a near infrared and an infrared area having wavelength of 800 nm or more is absorbed by an object and converted to a thermal energy. In addition, a large part of its energy distribution is converged at a near infrared area having a wavelength of 800-2000 nm. Accordingly, a film capable of selectively absorbing rays of a near infrared light is remarkably effective for cut-off of a solar energy, and its is possible to suppress an increase in temperature in a room admitting visible light. Such a film may be adapted to a window of a house, office, store, automobile and airplane, etc. as well as gardening green house. In particular, as to the green house, a temperature control is very important, and if temperature is excessively elevated, plants will be greatly damaged to finally result in withering. Accordingly, when the near infrared absorbing film is used, the temperature control may be rendered easy, and a new technique such as retarded cultivation in summer may be developed. A conventional heat radiation cutting-off material includes a thin metallic layer deposited on a surface of a plastic film or an inorganic compound, e.g., FeO dispersed in a glass.
(4) Cut filter of infrared rays noxious to tissues of human eyes:
Infrared rays contained in sun light or in light radiated in welding have a harmful influence to tissues of human eyes. One of the primary applications of the infrared cut filter is an application to spectacles for protecting the human eyes from rays of light containing such harmful infrared rays, e.g., sunglasses and protecting glasses in welding.
(5) Infrared cut filter for semiconductor light receiving element:
In another field where development of this kind of infrared absorbing plastics is most intensitively desired, the infrared absorbing plastics are adapted to an infrared cut filter for a photosensor to make the spectral sensitivity of a semiconductor light receiving element such as silicon photo diode (which will be hereinafter referred to as SPD) approach to a relative spectral sensitivity curve.
Presently, SPD is mainly used as a light receiving element of a photosensor used in an automatic exposure meter for a camera or the like. FIG. 2 shows a graph of the relative spectral sensitivity curve and that of a relative value of an output of SPD to each wavelength.
In order to use SPD for an exposure meter, it is required to cut-off a light in an infrared area which is not sensitive to human eyes and to make the spectral sensitivity curve of SPD shown in FIG. 2 approach to the relative spectral sensitivity curve. Particularly, as an output of SPD is large to the light having a wavelength of 700-1100 nm, and the eyes are insensitive to such a light, this is one of factors of malfunction of the exposure meter. Therefore, if it is possible to use an infrared absorbing plastic film suppressing an absorption of a visible light area, while permitting an absorption of an infrared light area in the entire range of 700-1100 nm, light transmittance in a visible area may be increased and an output of SPD may be also increased. Thus, it will be possible to apparently remarkably improve a performance of the exposure meter.
Conventionally, this kind of photosensor has been practically used by mounting an infrared cut filter made of glass containing an inorganic infrared absorbent to a front surface of SPD.
(6) Infrared cut-off filter for color solid pick-up element:
Recently, the combination of a color solid pick-up element and a micro color filter has been widely used for a camera for video tape recorder or the like. A photoconductive film and a solid pick-up element used for a usual pick-up tube are sensitive even in a wavelength area of 700 nm or more. Therefore, in order to separate a visible light having a wavelength of 400-700 nm, it is necessary to cut off near infrared rays of 700 nm or more. To this end, a near-infrared cut-off optical filter material has been conventionally used by forming a multi-layer interference film of inorganic materials on the surface of a lens by a vacuum evaporation process, but, differences between lenses are large. Then, if it is possible to form an infrared cut-off layer on a color separation filter layer by a lamination process or an on-wafer process, a satisfactory color reproduction may be expected without being influenced by the lens differences.
In this connection, it has been intensively desired to develop an infrared cut-off filter material to be incorporated in such a color pick-up tube and a color solid pick-up device using CCD (charge coupled device) and MOSFET (insulated gate type field effect device).
(7) Heat converter of visible and infrared rays:
The infrared absorbing material as a reaction acceleraor can be added to a thermodrying or thermosetting composition.
(8) Application to optical information recording medium for laser beam writing:
Conventionally, there are many known optical recording mediums for laser beam writing. The optical recording medium is typically formed by depositing a metal, metalloid or non-metal on a substrate by evaporation, or by depositing a dye by evaporation or coating the same on the substrate. Such application to a laser beam recording/reading medium is, for example, described in Japanese Patent Application (OPI) No. 11090/82.
However, with respect to the above-mentioned applications, the conventional infrared absorbing materials as used had the following shortcomings.
The safelight filter for the panchromic photosensitive material in the afore-mentioned applications (1) permits a green light having a high luminosity factor to be partially transmitted, and also permits a large quantity of infrared light to be transmitted to cause fogging. For this reason, such a safelight filter has not been able to achieve its object for infrared-senstive materials.
In the applications (3), the metallic layer deposited plastic film or the FeO dispersed glass functions to intensively absorb not only infrared light but also visible light to cause reduction in inside luminance. For this reason, such as plasic film or glass is not suitable for agricultural uses because of lack of an absolute quantity of sunshine. Especially, the filter material for growth control of plants in the applications (2) is required to selectively absorb a light having a wavelength of 700-750 nm, and therefore the metallic layer deposited film is quite unsuitable for such an object.
Furthermore, in the applications (5), the infrared cut filter using the infrared absorbent containing an inorganic substance is relatively fast to heat and light, but light transmittance in a visible area is low. To cope with this, a sensitivity of SPD was intended to be increased. However, an increase in the sensitivity of SPD results in an increase in leak current to cause a malfunction of the photosensor, resulting in a big problem in reliability. Additionally, since the infrared cut filter contains an inorganic substance, there is a lack in flexibility in production of a photosensor and a difficulty in improving a production process. Further, the infrared cut filter containing an inorganic substance causes a high production cost to result in a great increase in cost of the photosensor.
Furthermore, in the applications (8), the optical information recording medium prepared by depositing metal, etc. by vapor deposition had a defect in its productivity and was inferior in oxidation resistance and hydrolysis resistance of a recording layer. On the other hand, many of the optical information recording mediums prepared by coating or evaporations-depositing dyes did not have an absorption in a wavelength area of a semiconductor laser beam as used. Further even if the recording medium had an absorption in the wavelength area, weather resistance was not satisfactory. These optical information recording mediums were also not satisfactory in such that they had low sensitivity to a semiconductor laser beam and low stability.